The present invention relates to a steering axle arrangement for a non-driven steerable vehicle wheel, comprising a kingpin with a middle portion, which is fixed in a bore in an axle member, and with cylindrical ends extending above and below upper and lower surfaces of the axle member, a steering knuckle provided with an axle end for a wheel hub, and upper and lower taper roller bearings received in upper and lower bearing seats in the steering knuckle, in which said roller bearings cylindrical ends are mounted.
The most common type of steering axle arrangements for trucks has the steering knuckle itself mounted in a taper roller bearing at the upper end of the kingpin and in a journal bearing at its lower end. The upper bearing takes up both axial and radial forces, while the lower bearing only takes up radial forces. In such a steering axle arrangement, the axial forces on the upper bearing are dependent on the load, i.e. the axial load on the bearing varies with the gross weight of the vehicle. When taking a curve with a heavy load, the radial forces on the lower bearing can be so great that a certain gap will arise.
U.S. Pat. No. 4,798,394 describes a steerable axle assembly of the type described by way of introduction which also has a lower kingpin bearing in the form of a taper roller bearing which takes up both axial and radial forces. The taper roller bearings are preloaded with their bearing rings against an upper and a lower surface of the axle member. The outer ring of the lower bearing rests against a spacer ring which is held in place by a cover fixed by a number of screws. The preloading is regulated by an upper tightening screw which, via a washer, loads the inner ring of the upper bearing against the axle member. A design with preloaded roller bearings has the advantage that the bearing of the steering axle can be made entirely independent of load, so that variations in the gross weight of the vehicle only result in a redistribution between the axial forces on the bearings. More specifically, an increase in the load on the axle member, resulting in an increase in the axial forces on the upper bearing, will result in a corresponding reduction in the axial preloading in the lower bearing, whereby the level of friction in the bearing as a whole will be independent of load.